Adaptive noise cancellation requires at least two microphones and, under ideal conditions, at least one microphone must be placed at the noise source. This is not very practical for a person wearing a hearing aid. It is possible, however, to have both microphones mounted on the head with one microphone picking up more speech than noise and the other microphone picking up more noise than speech, as shown in Figure 5 (41,42). If the adaptive filter is used as before, the noise will not be cancelled completely but the level of the noise will be reduced. An improved speech-to-noise ratio will result, with improved intelligibility.


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